Rotary waveguide joint



United States Patent 0 ROTARY WAVEGUIDE JOINT Glenn A. Walters, Palo Alto, Calif., assignor to Dalmo Victor Company, San Carlos, Calif., a corporation of California Application June 29, 1951, Serial No. 234,317

2 Claims. (Cl. 333-98) This invention relates to a rotary waveguide joint for use in radio frequency equipment. Although the invention will be described with reference to radar equipment, the invention is obviously not limited to such use.

In radar practice, it is often necessary to rotate or oscillate the antenna relative to its associated apparatus. In order to allow for relative movement between the antenna and the apparatus, a rotary joint of some type is necessary. Prior rotary joints have been objectionable in that they have been complex in construction, expensive to manufacture and have required individual adjustment to enable them to successfully transmit the desired frequency band.

A main object of the present invention is to provide a rotary joint which is simple in construction, easy to manufacture, and therefore inexpensive, and which joint does not require adjustment for successfully transmitting the desired frequency band.

There is at present a demand for a rotary joint which can successfully transmit higher power than heretofore required. Prior rotary joints have reqquired the use of tuning buttons, resonant rings, matching windows and the like, all of which have been necessarily so positioned that electrical breakdown occurs between various of the parts when the power transmitted by the rotary joint is increased to the extent presently demanded.

A principal object of the present invention is to provide a rotary joint capable of successfully transmitting one megawatt of radio frequency energy without electrical breakdown, and which rotary joint eliminates the necessity for the expensive and complex contrivances provided in prior rotary joints.

Another object of the present invention is to provide a rotary joint which is broad band as compared to prior rotary joints and which rotary joint, though being broad band, is simple and inexpensive in construction and requires no adjustment to adapt it for use.

- A further object of the present invention is to provide a rotary joint for fulfilling the above named objects, which rotary joint is composed of two primary relatively rotatable parts, each part comprising a rectangular waveguide section fixedly secured and disposed at right angles to a circular waveguide section, said circular sections being coaxially disposed, said rotary joint having as the only means for enabling the proper transmission of radio frequency energy therethrough a step formation for each part, each step being disposed at the juncture of each circular section and the outer wall of its rectangular waveguide section.

Various other objects will be apparent from the following description taken in connection with the accompanying drawings wherein: a

Fig. 1 is a vertical mid-section through a rotary joint embodying the concepts of the present invention.

Fig. 2 is a horizontal sectional view taken along line 2-2. of Fig. 1.

Fig. 3 is a table of values for the dimension D shown in Fig. l.

2,708,263 Patented May 10, 1955 Generally speaking, rotary waveguide joints should be and are designed so that the impedance thereof is matched to the impedance of the input waveguide section to avoid undesirable effects on the magnetron or other radio frequency generating devices. The rotary joints are also so designed that the greatest possible amount of the power output from the radio frequency generating device is usefully employed. Stated in another way, when the standing wave ratio in a rotary joint is high, too much of the energy generated by the radio frequency generating device is reflected by the joint, consequently not being usefully employed, and also, having undesirable effects on the frequency generating device, such effects being well known in the art and not necessary here to describe.

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Further, a rotary waveguide joint should be so designed a that a higher percentage of the radio frequency energy in the circular waveguide section assumes a mode of circular symmetry, such as the TMOl, to avoid the disadvantages accompanying the creation of linearly polarized modes, such as the TEu mode. When linearly polarized modes exist or are created in the circular section of a rotary joint, the energy represented by the linearly,

However, as previously mentioned, these prior joints,

were complex, expensive, and in general had to be individually adjusted. One of the most common types of prior rotary joints is disclosed in Volume 9 of the M. l. T. Radiation Series, page 393, Fig. 0, which rotary joint is widely used at the present time. It will be noticed that the identified waveguide joint disclosed on page 393 utilizes a tuning button, resonant rings, and what might be termed a full step formation formed at juncture of a circular waveguide section and the outer wall of its rectangular waveguide section. As previously mentioned, it is desirable in the present invention to eliminate contrivances such as tuning buttons and resonant rings and provide a simple rotary waveguide joint which can be easily and inexpensively manufactured and has the de sirable characteristics set out hereinbefore. waveguide joint of the present invention fulfills the above requirements.

Referring to the accompanying drawings, wherein similar reference characters designate similar parts throughout, the rotary waveguide joint includes two main parts, 9 and 11, which are rotatable relative to one another. Part 9 has a rectangular input waveguide section 13 formed integrally with and disposed at right angles to a circular waveguide section 15. Part 11 likewise has a rectangular output waveguide section 17 formed integrally with and disposed at right angles to a circular waveguide section 19. Circular waveguide sections 15 and 19 are coaxially arranged and connected for relative rotatable movement by a bearing 23 suitably retained in place by a split ring 21. 0 rings 25 are preferably provided between the bearing races and the circular waveguide sections 15 and 19 as shown. I

Whereas in prior rotary joints, a plurality of devices or contrivances were provided to enable the rotary joint to successfully transmit radio frequency energy, in the present invention only a single step formation for each primary part of the rotary joint is required, the step for part 9, being given the reference numeral 31 and the The rotary step for part 11, being given the reference numeral29.

Each step formation takes the shape of a crescent as clearly shown in Fig.2, the radius of the convex boundary of each crescent being the radius of the interior of the circular waveguide sections and the radius of the concave boundary of each crescent being equal to one-haif the width of the rectangular waveguide sections. It is pointed out that the step formations are true crescents so that the'end portions thereof regularly and progressively'taper to their ends toprovide a step presenting of 'the inner wall of its rectangular waveguide section.

in order to provide a workable rotary joint, it is extreniely important that the step terminate short of and be spaced from the mentioned plane, otherwise there is alack of matching between the impedances in the cir-- cnlar and rectangular waveguide sections, and also the creation of an unwarranted amount of the T1311 mode in the circular section, the TEu mode being linearly polarized and objectionable for reasons well known in the art and briefly previously referred to.

'More specifically, with relation to the rotary waveguide joint shown, when radio frequency energy having a'frequency of 9,300 megacycles and a power output of one megawatt was imposed on the rotary joint, there was achieved a standing Wave ratio of less than 1.15 and a'production of the T541 mode in the circular section in an amount less than 5%, which production of TEll mode energy was not found objectionable. 7

Certain primary dimensions of a rotary waveguide joint for transmitting radio frequency energy having a frequency of substantially 9,300 megacycles are given on the drawing to effect a full disclosure of the present invention. Once these dimensions are given, a rotary joint. for a different band of radio frequency energy can easily be constructed by simple scaling and interpolation.

Where tolerances are not given, they are l or minus .005 inch, except in the case of the dimension for the rectan lar wav g id whi h i s andar Y 1%" by 1 wall thickness rectangular waveguide. The critical nature of the step dimensions are apparent from the tolerances given these dimensions.

It is pointed out that by designing a step having the dimensions shown in the drawing and terminating short of the mentioned planeQthe resonant rings and, tuning button necessary in prior waveguide joints have been eliminated. ture of thestep terminating short of the, mentioned plane is extremely important, it is likewise important that the relationship of the height of the step to the maximum depth or thickness of the step be that as disclosed in the drawings in order to provide a successful rotary waveguide joint. In other words, merely terminating the step at the place disclosed in the drawing would not of itself provide a successful rotary joint, but, the step must be terminated as shown and must have a maximum depth or thickness substantially that disclosed in the drawing or a proportion thereof. It is here repeated that the dimensions given in. the drawing are for a particular radio frequency band, and the invention is not intended to be limited to the specific dimensions, since when using a different frequency-band, the dimensions can be changed by a simple scaling operationto obtain a rotary joint capab frequency band.

It s thenpq n e o hatw tb the r t ry j n of f the present invention, there will be no electrical break- It is also pointedout that althoughthe fear le of properly transmitting the newly selected radio down across any of the parts of the joint becausethe onlyparts required are spaced sufliciently far apart to prevent an electrical breakdown even when the joint is transmitting one megawatt of radio frequency energy.

The rotary waveguide joint of the present invention can obviously be simply manufactured since the steps thereof can be easily machined by simple turning operations. There are no adjustable devices or contrivances to be manufactured or adjusted, thereby eliminatingthe time and expense of providing the adjustable devices and thereafter adjustingsuch devices. With the rotary waveguide joint as disclosed in the drawings-and using the frequency and power output stated, a width of approximately 4% was achieved which when compared to most prior rotary Waveguide joints makes the present rotary joint a broad bandrotary joint.

Having thus described my invention, what I claim and V desire to secure by Letters Patent is:

1 In a rotary waveguide joint having a pair of opposed coaxially arranged relatively rotatable circular waveguide sections to each of which is joined at the outer end thereof at right angles thereto, a rectangular waveguide section, the improvement which comprises the provision of a single step for each joined unit disposed in the interior corner at the juncture of-the parts of each unit and serving as the sole means for insuring the proper transmission of radio frequency energy through the rotary joint, said steps being crescent shaped and facing'in the direction of extension of their respective associated rectangular waveguide sections, the. ends of each step regularly and progressively blending into the parts of its joined unit, the exterior corner of the step being rounded, said joint having the following dimensions when constructedto pass radio frequency energy at 9300 megacycles, and proportionally dimensioned when transmitting radio frequency energy at other frequencies, said rectangular waveguide sections each having interior dimensions of 1 /8 inches by /2 inch, each circular section having an interior diameter of 1 6 inches, each step extending inwardly from the innersurface of the bottom of the rectangular waveguide a distance of substantially .350 inch, the interior arc of the crescent having a radius of of an inch taken from a center disposed substantially .160 inch off center from the axis of the circular sections in the direction of the rectangular waveguide.

2. In a waveguide joint having a circular waveguide section joined at one end to a rectangular waveguide section, the improvement which comprises theprovision of a single step disposed in the interior corner at the juncture of the parts and serving as the sole means for insuring the proper transmission of radio frequency energy from the rectangular section to the circular section or vice versa, said step being crescent shaped and facingin the direction of extension of the rectangular waveguide section, the ends of the step regularly and-progressively blending into the rectangular waveguide section, said joint having the following dimensionswhen constructed to pass radio frequency energy at'9300 megacycles; and

being proportionally dimensioned when transmitting radio frequency energy at other frequencies, said rectangular waveguide having interior dimensions of 1% inches by /2 inch, said circular section having aninterior diameter of 1% inches, said step extending inwardly from the inner surface of the bottom of'the; rectangular waveguide a distance of substantially .350 inch, theinterior arc of the crescent having a radius of hi inch-taken from a center disposed substantially .16 0 inchofi center from the axis of the circular section inthe direction of the rectangular waveguide.

References .Cited'iu the-file ofthis patent Publication Microwave Transmission Circuits,by,

Ragan, vol, 9 of Radiation Laboratory'Series, published by McGraw-Hill in 1948'. Copy in Div. 69: i 

